EP4170366A1 - Method for assessing an electrical storage cell - Google Patents

Abstract

The invention relates to a method for assessing an electrical storage cell (2), comprising at least the following steps: a) creating a reference data set (4) on the aging behavior of an individual reference storage cell (6) of a specific type with regard to its charging and discharging behavior, b) Creation of a second reference data set (4') of a second reference memory cell (6') of the same type c) Measuring an electrochemical operating characteristic (8, 8') of each reference memory cell (6, 6') for which a reference data set (4, 4') is created and linking this operating characteristic (8, 8') with its reference data set (4, 4')d) storing at least two reference data sets (4, 4') of at least two reference memory cells (6, 6') of the same type and the associated links of Operating characteristics (8, 8') in a database (10),e) measuring the electrochemical operating characteristics (8") of a storage cell (2) andf) comparing the measured operating characteristics (8") of the storage cell (2) with those in the database ( 10) stored operating characteristics (8, 8') of the reference memory cells (6, 6') andg) assignment of the memory cell (2) using an assignment key to one of the operating characteristics (8, 8') saved in the database (10) and the associated link reference data set (4, 4').

Description

The invention relates to a method for evaluating an electrical storage cell according to patent claim 1.

The operational control of batteries and battery cells benefits in important areas (service life, costs, etc.) from the most precise possible knowledge of the connection between the form of use and aging. An important description of this relationship are sets of aging curves, which are sometimes also called Wöhler curves based on an equivalent from mechanics, in which the expected service life is assigned to a cycle depth (DoD).

Determining these sets of aging curves using conventional methods is very expensive and sometimes even involves the destruction of the memory cell to be tested. In this case, for example, the maximum possible number of charging cycles is measured for a cell at different depths of discharge (DoD) and different states of charge (SoC) until the corresponding memory cell is defective. This is in turn repeated for each data point of the set of curves with a large number of memory cells, and a mean value is determined from the tested memory cells for each point. It is understandable that this procedure is useful for drawing conclusions as to the load range in which a type of memory cell should typically be used. However, this family of curves must be prepared for each type of storage cell, and minor changes in the design and construction or production generally require the preparation of a corresponding family of aging curves.

There is therefore a conflict of interest with the desire to be able to assign such a measurement to each delivered storage cell individually and thus enable optimal control/regulation of each battery. Alternatively can Such a measurement can be assigned to the respective building type in a generalized way, without taking into account the individual variances.

The object of the invention is to provide a test method for a storage cell in which the storage cell is only slightly loaded and which allows a high level of information about its individual electrochemical characteristics.

The solution to the problem consists in a method for evaluating a memory cell with the features of patent claim 1.

1. a) Erstellen eines Referenzdatensatzes über das Alterungsverhalten einer einzelnen Referenzspeicherzelle eines bestimmten Typs in Bezug auf ihr Lade- und Endladeverhalten,
2. b) Erstellen eines weiteren Referenzdatensatzes einer zweiten Referenzspeicherzelle desselben Typs
3. c) Messen einer elektrochemischen Betriebscharakteristik einer jeden Referenzspeicherzelle, zu der ein Referenzdatensatz erstellt wird und Verknüpfen dieser Betriebscharakteristik mit dem jeweiligen Referenzdatensatz
4. d) Hinterlegen von mindestens zwei Referenzdatensätze mindestens zweier Referenzspeicherzellen desselben Typs sowie die dazugehörigen Verknüpfungen der Betriebscharakteristik in einer Datenbank,
5. e) Messen der elektrochemischen Betriebscharakteristik einer Speicherzelle und
6. f) Vergleich der gemessenen Betriebscharakteristik der Speicherzelle mit den in der Datenbank hinterlegten Betriebscharakteristiken der Referenzspeicherzellen und
7. g) Zuordnung der Speicherzelle an Hand eines Zuordnungsschlüssels zu einem der in der Datenbank hinterlegten Betriebscharakteristiken und dem damit verknüpften Referenzdatensatz.

The method according to patent claim 1 has the following method steps.

1. a) Creation of a reference data record on the aging behavior of an individual reference memory cell of a specific type with regard to its charging and discharging behavior,
2. b) Creation of a further reference data record of a second reference memory cell of the same type
3. c) Measuring an electrochemical operating characteristic of each reference storage cell for which a reference data set is created and linking this operating characteristic to the respective reference data set
4. d) depositing at least two reference data sets of at least two reference memory cells of the same type and the associated links of the operating characteristics in a database,
5. e) measuring the electrochemical operating characteristics of a storage cell and
6. f) comparison of the measured operating characteristics of the memory cell with the operating characteristics of the reference memory cells stored in the database and
7. g) Allocation of the memory cell using an allocation key to one of the operating characteristics stored in the database and the reference data record linked thereto.

The advantage of the method described over the prior art is that the aging curves in the form of the mean value-based reference data set are not carried out for a large number of memory cells and no mean value is formed from the measured values or measured curves of the individual reference memory cells. Instead, only one reference memory cell is used in each case, from which a reference data record on its aging behavior is created in each case. The information on the reference memory cell (reference data set) is also linked to an electrochemical operating characteristic determined by measurement.

The term two or more memory cells “of the same type” means that the memory cells are essentially structurally identical, but differ within the scope of production tolerances. In particular, the electrochemical composition of the individual storage cells is the same within the manufacturing tolerances. The reference memory cells and the memory cells evaluated using the method are accordingly of the same type.

Furthermore, storage cells under consideration, which are tested for their characteristics, for example after their production, only have to be checked for an electrochemical operating characteristic which can be determined in a technically relatively simple manner and which only minimally loads the cell. From the stored database, in which a plurality (at least two) of tested reference memory cells are stored with their respective reference data sets on aging behavior and corresponding operating characteristics, the reference data set that best matches the operating characteristics of the memory cell under consideration can be inferred. It has been found that storage cells with similar electrochemical operating characteristics exhibit similar aging behaviors. Therefore, the link between two memory cells with similar Operating characteristics suitable for inferring the aging behavior of the corresponding reference memory cell and its reference data set with a sufficiently good approximation and using this for the memory cell under consideration.

After considering this best-possible match, the storage cell can be specified for use in a battery storage system, for example and preferably. Or the storage cell under consideration can be linked to a control or regulation instruction that is optimal for it, which can then be taken into account individually when the cell is later installed in a larger system.

In a further embodiment of the invention, three variables are linked together for data points of the reference data set on the aging behavior, namely a depth of discharge (DoD), a state of charge (SoC) and a number (N) of the equivalent full cycles of the reference memory cell possible for this. Equivalent charging cycles mean the following, e.g. 10 charging cycles at 10% correspond to an equivalent full cycle, analogously 4 cycles at 25% would be an equivalent full cycle. Such a combination of data points results in a very large amount of information when transferred to the further control of the memory cell under consideration. It is useful to include at least 5 such data points in a reference data set. This means that the maximum charge cycles of the reference memory cell should preferably be determined for at least five combinations of SoC and DoD.

In addition or as an alternative, it would also be possible to include the current intensity of the charging or discharging current and/or the temperature during the charging or discharging process as data points in the reference data set.

The number of reference memory cells considered and the resulting number of corresponding reference data sets should naturally be relatively high in order to have the greatest possible selection for the best possible assignment of its operating characteristics for each memory cell under consideration. On the other hand, the high level of technical complexity and thus also the high costs speak for the lowest possible number of reference data sets for reference memory cells, which is why at least two reference memory cells are considered and stored in the database, with there being preferably at least five reference memory cells whose reference data sets are stored in the database become. With at least 20 reference data sets from 20 reference memory cells, one has a very good selection of reference data sets for a good allocation of the checked memory cells.

In a preferred embodiment of the invention, the following method is used to create the reference data sets for the aging behavior of the reference memory cells. The method for determining at least one average capacity loss of a reference memory cell comprises a number of steps. In a first step a), at least two load cycles of the battery storage device are measured using a high-precision coulometry device (HPC), with a single load cycle comprising a first discharging, in which a first amount of charge is measured from a first state of charge to a second state of charge becomes. A subsequent first charging takes place, in which a second quantity of charge is measured from the second charge state to a third charge state. A second discharging then takes place, in which a third amount of charge is measured from the third charge state to a fourth charge state. Charging and discharging in the load cycle take place between a lower voltage and an upper voltage of the battery storage. In a second step b), a first charge transfer is determined using a difference between the fourth charge state and the second charge state and a second charge transfer is determined using a difference between the third charge state and the first charge state. In a third step c), a capacity loss is determined from the difference between the first charge transfer and the second charge transfer, the first step a), the second step b) and the third step c) being carried out until the capacity loss is essentially constant . The mean capacity loss is then determined based on at least two capacity losses.

The method described, which is referred to below as the HPC method for simplification, has the advantage over the prior art that conclusions can be drawn about the maximum charge cycles of a reference memory cell as a result of significantly fewer charging and discharging processes. It is thus possible, using the method described, to obtain meaningful values about the aging behavior of the reference memory cell much more quickly without destroying it in any case. The HPC method makes it possible to obtain groups of aging curves or reference data sets for reference memory cells much more quickly and to display them in detail.

In a further embodiment of the invention, the electrochemical operating characteristics are determined in the form of electrochemical impedance spectroscopy (EIS). The EIS is an established technical process that can be applied to storage cells without great technical effort and hardly burdens them with regard to their aging. The EIS is a method that can be applied by default to any memory cell after fabrication. The EIS is usually represented graphically in the form of a Nyquist diagram. This display method for impedances, which is common in electrical engineering, shows, for example, the real part of the impedance value displayed as a complex number on the x-axis and the imaginary part of the impedance value on the y-axis.

It can also be expedient here for the determination of the electrochemical operating characteristics to be taken into account discrete frequencies of an impedance spectrum obtained by means of impedance spectroscopy. For this purpose, for example, one to three frequencies characteristic of the electrochemical behavior of the storage cell could be recorded and evaluated. This does not require the creation of an entire impedance spectrum, which saves time and manufacturing costs. The term discrete is understood to mean that a very narrow but not infinitely narrow frequency range is considered, which can be viewed using conventional technical methods.

An alternative possibility or an additional possibility to test the electrochemical operating characteristics of a storage cell would be an HPC method as described in patent claim 4 . In this case, if necessary, fewer iteration steps would be carried out than is the case in the production of the reference data set described. In particular, only one data point of the reference data record that is as characteristic as possible could be measured. The lower number of iterations would result in a lower load on the memory cell and a correlation to the reference data record could nevertheless be brought about on the basis of the value measured in this way.

A further advantageous embodiment of the invention consists in that electrochemical quality classes are defined for the memory cells and after the memory cell has been assigned to a reference data set, the memory cell is assigned to a quality class. As a result, the memory cells can be built into defined memory units when they are used, either sorted according to their quality class. The memory units assembled in this way have different performance classes, for example. On the other hand, it is possible to drive the memory cells in a memory unit individually according to their assigned quality class. For example, a memory cell that can be expected to have a higher number of full cycles can be specifically charged singularly when the memory unit is under medium load and discharged, while weaker storage cells are in turn spared more often.

A further advantageous embodiment of the invention consists in the maximum number of equivalent full cycles in the reference data set serving as quality criteria for the quality classes. As described, this can be used, for example, for targeted driving of the memory cells in the memory unit. As an alternative or in addition to the maximum number of full cycles, the quality criteria can be characterized by the volume under the family of curves that is formed by the reference data set. This criterion can also be viewed as the mean number of possible full cycles over all data points of the reference data set.

Further embodiments and further features of the invention are explained in more detail with reference to the following figures. These are schematic representations and exemplary configurations that do not represent a restriction of the scope of protection.

Figur 1

eine Alterungskurvenschar für einen Typ von Speicherzellen nach dem Stand der Technik, bei dem für jedem Punkt der Kurvenfahrt mehrere Speicherzellen untersucht sind.

Figur 2

im oberen Teil einen Referenzdatensatzes des Alterungsverhaltens einer einzelnen Referenzspeicherzelle und im unteren Teil eine korrespondierende Darstellung einer EIS Messung derselben Zelle.

Figur 3

die zu Figur 2 analoge Darstellung des Referenzdatensatzes einer weiteren Referenzspeicherzelle und

Figur 4

die zu den Figuren 2 und 3 analoge Darstellung des Referenzdatensatzes einer wieder anderen Referenzspeicherzelle.

Figur 5

eine schematische Darstellung einer praktischen Anwendung der Kombinationen des Referenzdatensatzes und der Betriebscharakteristik.

show:

figure 1

a family of aging curves for a type of storage cell according to the prior art, in which several storage cells are examined for each point of cornering.

figure 2

in the upper part a reference data set of the aging behavior of a single reference memory cell and in the lower part a corresponding representation of an EIS measurement of the same cell.

figure 3

the to figure 2 analog representation of the reference data set of a further reference memory cell and

figure 4

the to the Figures 2 and 3 analog representation of the reference data record of yet another reference memory cell.

figure 5

a schematic representation of a practical application of the combinations of the reference data set and the operating characteristic.

In the figure 1 a family of aging curves 24 for electrical storage cells according to the prior art is shown. The ratio of the depth of discharge (DoD) and the state of discharge or state of charge (SoC) is plotted in one plane. The number of possible maximum charging cycles for the respective points with regard to DoD and SoC is plotted in the Z direction, denoted by N. The graphic shows that with a very low depth of discharge of 5%-10% around an average state of charge SoC of between approx. 40 and 60%, the highest number of charging cycles can be achieved. The deeper the memory cell is discharged, i.e. the higher the DoD, the lower the number of charging cycles until the memory cell is destroyed.

The special thing about the graphic according to figure 1 consists in that for each individual data point 26 shown there, a plurality of memory cells are subjected to this procedure and the data point 26 represents a nominal mean value from the values obtained for all memory cells considered. For this reason, the method described is technically very complex and it has to be created anew for each individual type of memory cell. Therefore, for economic reasons, the number of data points 26 in the family of aging curves 24 is kept very small, which is why such family of curves 24 often only have little meaningfulness. Furthermore, all data points 26 are mean values, so that in the case of a memory cell under consideration, which is removed from production, it can only be concluded on average how it will behave in the corresponding DoD and SoC combinations. an individual Consideration of a storage cell and thus a load control tailored to this cannot take place on the basis of the curve arrays 24 according to the prior art.

In the Figures 2 to 4 sets of curves are shown that correspond to the set of aging curves 24 figure 1 fundamentally very similar, but differ significantly from them. The difference in the sets of curves in the Figures 2-4 , which are referred to there as reference data sets 4, 4', consists in the fact that said reference data set 4 or 4' is prepared for a reference memory cell 6, 6' removed from production. Data points 14 in the representations according to FIG Figures 2, 3 and 4 are not mean values from a number of memory cells, but rather the results of measurements from a singular reference memory cell 6, 6'. It should be noted here that the reference memory cell 6 is also used in the following to distinguish that it is not an identical memory cell. If further reference symbols 6' are used, these are in turn further individual memory cells which also differ from one another. This terminology applies both to the reference data set 4, the reference memory cells 6 and the operating characteristic 8 to be described.

An electrochemical operating characteristic 8, 8', by which the reference memory cell 6, 6' is characterized, is now preferably recorded for the respective reference memory cell 6, 6' before the preparation of the reference data set 4, 4'. So-called electrochemical impedance spectroscopy 16 has turned out to be the preferred operating characteristic around 8 . The impedance spectroscopy 16 is preferably applied in the form of a Nyquist diagram 12 and is in each case Figures 2, 3 and 4 shown in the lower part. The real part of the impedance Z is shown on the X-axis and the imaginary part is shown on the Y-axis. This results in a characteristic operating characteristic 8, 8' for each reference memory cell 6, 6', which in turn is unique a reference data record 4, 4' can be assigned to this individual reference memory cell 6, 6'.

This assignment applies to all reference data sets 4, 4 ', the example in the Figures 2, 3 and 4 are shown. Here it can be seen that all 3 in the Figures 2, 3 and 4 The reference data sets shown do show individual changes, even if they are essentially qualitatively similar. In the Figures 2 to 4 only 3 different reference data sets 4, 4' are shown. In order to be able to assign electrical storage cells 2, which originate from ongoing production, to the reference data sets 4 as well as possible, it is expedient to have the highest possible number of reference data sets 4 and the correspondingly assigned resource characteristics 8. At least five, preferably more than 20 such pairings should be made. It also applies to the number of data points 14 in the individual reference data records 4 that the greatest possible number of data points 14 should be present. A minimum is seen here at five data points 14, preferably more than 20 data points are also prepared.

A conventional test series of discharging and charging processes, which ultimately lead to the destruction of the reference memory cell 6, can be used to create the data points 14 in the method described. However, within the scope of optimizing the technical effort, the HPC method already described can be used. In this way, the reference data record 4 is created with significantly less technical effort. The HPC method described can also be used as an alternative or in addition to the impedance spectroscopy method 16 as the operating characteristic 8 with a small number of iteration steps.

In the figure 5 a practical application of the combinations of reference data set 4 and operating characteristic 8 is shown schematically. Here are in the upper part of the figure 5, a plurality of reference memory cells 6, 6′ have been examined, and a reference data set 4 and an operating characteristic 8 corresponding thereto are produced and displayed by means of an impedance spectroscopy 16. The total number of the combination of reference data records 4 and operating characteristics 8 of each examined reference memory cell 6 are stored in a database 10, which is figure 5 is indicated as a dashed box around the total number of counts.

If a large number of storage cells 2 from production are now examined for their electrochemical characteristics, which in figure 5 is indicated in the lower part using a conveying path 18 on which a large number of storage cells 2 are conveyed, each individual storage cell 2 is preferably examined with regard to its operating characteristics 8 . this is in figure 5 indicated schematically by means of a robot device 20. This means that an electrochemical impedance spectroscopy 16 is preferably produced for each storage cell 2 . The preparation of the impedance spectroscopy 16 hardly means any electrochemical stress worth mentioning for the storage cell 2 and thus provides an operating characteristic 8 which is compared with the operating characteristics 8 8 ′ in the database 10 . Here, an assignment key 22 is used figure 5 is indicated by the dashed double arrow. The assignment key can be an artificial intelligence programming specially designed for the corresponding graphs, which searches for the best possible similarities and matches according to empirical criteria. If the greatest possible match between the measured operating characteristic 8 of the memory cell 2 and an operating characteristic 8 from the database 10 has been determined, then an aging process according to the associated reference data set 4 can be inferred with good accuracy.

The advantage of the method is that for any memory cell 2 after production with a high Accuracy an individual family of aging curves in the form of the reference data set 4 can be assigned. These are not probabilities that are formed from mean values, based on which the type of memory cell specifically ages, but rather individual predictions can be made for the individual memory cell 2 under consideration. This is where the method described differs explicitly from the prior art, in which only average probabilities for the aging behavior are given.

This in turn gives rise to the possibility that an individual load control can also be assigned to each individual storage cell 2 in its use. i.e. in the case of a storage cell 2 which is individually designed to be somewhat weaker in terms of its aging behavior than another, individual storage control can take place in a later storage system by finally installing it. This means that even in a complex storage system, individual storage cells can be treated individually so that they can be optimally controlled according to their individual performance and aging conditions. As a result, a longer service life can also be achieved for the corresponding storage system, for example a storage unit for an electric vehicle. On the other hand, with the knowledge about the individual aging properties of each individual storage cell 2, it is also possible to put together storage systems with particularly high performance characteristics, so that storage systems which are structurally identical when viewed from the outside can be used with different performance classes in terms of their requirements. For example, an electric vehicle with a higher performance label can have a higher performance—possibly only for a short time—with the same design of the energy storage system if correspondingly sorted storage cells 2 are combined in this storage system.

Reference List

2

electrical storage cell

4

reference record

6

reference memory cell

8th

electrical chemical operation characteristics

10

Database

12

Nyquist chart

14

data points

16

electrochemical impedance spectroscopy

18

conveyor line

20

robotic device

22

mapping key

24

aging curve show

26

averaged data points

DoD

depth of discharge

SoC

state of charge

Claims (12)

Method for evaluating an electrical storage cell (2), comprising the following steps, a) Creation of a reference data record (4) on the aging behavior of an individual reference memory cell (6) of a specific type with regard to its charging and discharging behavior, b) creating a second reference data set (4') of a second reference memory cell (6') of the same type, c) Measuring an electrochemical operating characteristic (8, 8') of each reference storage cell (6, 6') for which a reference data set (4, 4') is created and linking this operating characteristic (8, 8') with its reference data set (4, 4'), d) storing at least two reference data records (4, 4') of at least two reference memory cells (6, 6') of the same type and the associated links of the operating characteristics (8, 8') in a database (10), e) measuring the electrochemical operating characteristics (8") of a storage cell (2) and f) Comparison of the measured operating characteristics (8") of the memory cell (2) with the operating characteristics (8, 8') of the reference memory cells (6, 6') stored in the database (10) and g) Allocation of the memory cell (2) using an allocation key (22) to one of the operating characteristics (8, 8') stored in the database (10) and the reference data record (4, 4') linked thereto. Method according to Claim 1, characterized in that data points (14) of the reference data set (4, 4') relating to the aging behavior link three variables to one another, namely a depth of discharge (DoD), a state of charge (SoC) and a number of the equivalent full cycles possible for this ( N) the reference memory cell. Method according to Claim 2, characterized in that the reference data set (4) contains at least five data points with links between the three variables. Method according to one of the preceding claims, characterized in that at least five reference data records (4, 4') with the respectively corresponding operating characteristics (8, 8') are stored in the database (10). Method according to one of the preceding claims, characterized in that the reference data set for the aging behavior is created using the following methods: a) Measuring at least two load cycles of the battery storage device using a high-precision coulometry device, wherein a load cycle comprises a first discharging, in which a first amount of charge is measured from a first state of charge to a second state of charge, a subsequent first charging, in which a second amount of charge is measured from the second state of charge to a third state of charge and a second discharging, in which a third amount of charge is measured from the third state of charge to a fourth state of charge, the charging and discharging of the duty cycle between a lower voltage and an upper voltage of the battery storage takes place b) determining a first charge transfer using a difference between the fourth charge state and the second charge state and determining a second charge transfer using a difference between the third charge state and the first charge state, c) determining a capacity loss from the difference between the first charge transfer and the second charge transfer, - Carrying out steps a) to c) until the capacity loss is almost constant in at least two consecutive load cycles, - determining an average capacity loss based on at least two capacity losses. Method according to one of the preceding claims, characterized in that the electrochemical operating characteristic (8) is determined in the form of an electrochemical impedance spectroscopy (16). Method according to Claim 6, characterized in that the determination of the electrochemical operating characteristic takes place by considering discrete frequencies of an impedance spectrum obtained by means of impedance spectroscopy. Method according to one of Claims 1 to 5, characterized in that the electrochemical operating characteristic (8) is determined by means of a method according to Claims 5 a) to 5 c). Method according to one of the preceding claims, characterized in that after a memory cell has been assigned to a reference data set, the use of the memory cell in a battery storage system is specified. Method according to one of the preceding claims, characterized in that electrochemical quality classes for the storage cells (2) are defined and after the allocation of the storage cell to a reference data set (4, 4'), the storage cell (2) is assigned a quality class. Method according to Claim 10, characterized in that quality criteria for the quality classes are characterized by the maximum number of equivalent full cycles in the reference data set (4). Method according to one of Claims 10 or 11, characterized in that the quality criteria are characterized by the volume under the family of curves which is formed by the reference data set.

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